1. Technical Field of the Invention
The present invention relates to a method and an apparatus for treating high chlorine concentration chlorine bypass dust that is recovered from a chlorine bypass system attached to a cement manufacturing facility.
2. Description of the Related Art
Chlorine bypass systems have been used to remove chlorine that may cause troubles such as preheater clogging in cement manufacturing facilities. In recent years, recycling of waste through conversion to cement raw material or fuel has been promoted, which increases the quantity of volatile matters such as chlorine, and the quantity of chlorine bypass dust generated as the quantity of the treated waste increases, which necessitates developments of methods for effectively utilizing the chlorine bypass dust.
From the above-mentioned point of view, in a treatment method through conversion to cement raw material described in Patent Documents 1 and 2, to wastes containing chlorine is added water to allow the chlorine in the wastes to be eluted and filtrated; desalted cake obtained is utilized as a cement raw material; pH of waste water is adjusted to precipitate heavy metals and collect them; and the waste water from which heavy metals are collected is discharged after salt is recovered therefrom or as it is.
However, in the above-mentioned invention described in the Patent Documents 1 and 2, heavy metals remain in a desalted cake, and sludge recovered in waste water treatment contains heavy metals also, therefore, when the desalted cake and the sludge are returned to a cement raw material system, heavy metals are concentrated in a cement burning system while circulating therein, which may cause problems such as increased chemical cost for waste water treatment and increased concentrations of heavy metals in clinker.
On the other hand, in a method and an apparatus for treating chlorine bypass dust described in Patent Document 3, slurry obtained by adding water to a chlorine bypass dust is stored, the stored slurry is fed to a cement finishing process together with at least one selected from the group consisting of clinker, gypsum and admixture, and those are crushed while being mixed in a mill for cement production. With this method, heavy metals contained in the chlorine bypass dust is not concentrated while circulating in the cement burning system, which prevents increases in the chemical cost and concentrations of heavy metals in clinker described above.
Patent document 1: Japan Patent No. 3304300 gazette
Patent document 2: Japan Patent No. 4210456 gazette
Patent document 3: Japan Patent No. 4434361 gazette
However, in the treatment method described in Patent Document 3, water is added to the chlorine bypass dust to generate slurry, which causes CaO in the chlorine bypass dust to be converted to Ca(OH)2 through slaking. Therefore, CaO, Ca(OH)2 and CaCO3 that are unreacted and remain as calcium compounds exist in a mixed state in the slurry, so that when this slurry is fed to a cement finishing process, CaO and Ca(OH)2 contents in produced cement fluctuate, which may affect properties such as setting time.
The present invention has been made in consideration of the above problems in the conventional art, and the object thereof is to treat chlorine bypass dust while preventing increases in chemical cost and concentrations of heavy metals in clinker, and ensuring stability in quality of cement.